The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art.
A typical motor vehicle automatic transmission includes gear elements and multiplate clutches that are selectably engageable to establish one of several forward speed ratios between the transmission input and output shafts. The input shaft may be coupled to the vehicle engine through a fluid coupling such as a torque converter, and the output shaft may be coupled to the vehicle drive wheels through a differential gear set.
A multiplate clutch generally includes a set of core plates, usually bearing friction material, a set of separator (or reaction) plates, and a hub, all of which are housed in a clutch case. Spline grooves in the clutch case engage with splines along the outer periphery of either the separator plates or the core plates. Another set of spline grooves in the hub engage with splines around the inner surfaces of either the core plates or the separator plates, i.e., whichever of the plates are not splined to the case are splined to the hub. The separator plates and the core plates are arranged alternately so that they can be engaged or disengaged with each other.
When the multiplate clutch is engaged, the separator plates and the core plates are pushed together, they contact each other and rotate (or are fixed) together, thereby coupling the clutch case and hub to which the plates are attached. When the multiplate clutch is disengaged, the separator plates and the core plates are no longer pushed together, and therefore, the separator plates and the core plates theoretically rotate independently of each other. Sometimes, however, the core plates stick to the separator plates or otherwise remain at least partially contacting the separator plates, even when the multiplate clutch is disengaged. This may result in drag and spin losses within the multiplate clutch. Therefore, it is desired that that core plates and the separator plates fully disengage and separate from each other when the multiplate clutch is disengaged.